IceNine[note 1] is Dave Greene's name for a hypothetical unstoppable quadratic growth pattern that expands outward through random ash at speed c/137, described as follows in a tongue-in-cheek post in February 2008:
|“||Aha! You and your intuition have clearly not been exposed to the IceNine Agar, found recently with an alternate-universe oscilloscope:
#C IceNine seed -- currently this is the smallest sample #C for which no external conditions have yet been found #C that prevent long-term quadratic growth x = 2718, y = 4669, rule = B3/S23 <<<Server notice from fermat.yahoo.com: 11.9MB nonstandard text removed from message Please notify sender of potential virus threat>>>
Every sufficiently large and ancient B3/S23 universe observed so far turns out to be full of this weird agar, which expands in all directions through random ash at c/137. IceNine seems to absorb blocks and blinkers particularly well, due to a complicated froth of sparks at its front lines -- not generated by glider collisions, but by a lucky accident of the agar's internal structure.
When the expanding front touches an active pattern that it can't immediately annihilate, the pattern "dies back" a short distance at near lightspeed, leaving behind a protective scattering of blocks; behind the blocks the front stabilizes and starts expanding again. Converging IceNine fronts usually cause small diebacks that stabilize as small defects in an apparent quasicrystalline structure.
And before you all ask, my alternate-universe oscilloscope was repossessed by the Outsiders the other day, so unfortunately I can't lend it out. But there didn't seem to be anything but IceNine out there anyway --
He went on to further characterize IceNine as follows:
|“||The IceNine I tried to describe doesn't have a memory per se, any more than a cell's DNA knows the position of every lipid molecule in its cell wall. It's an active, growing agar with lots of edge sparks that just happen to annihilate nearby gliders and still lifes unusually efficiently. Along with several other utterly improbable properties. Basically it's the spacefiller that wins the Survival of the Fittest Award in an infinite Life universe, and it's about as likely as the proverbial tornado in a junkyard building a jumbo jet.||”|
It is generally agreed that a pattern exhibiting the characteristics of IceNine cannot exist in Conway's Game of Life, but a formal proof remains elusive.
- Adam P. Goucher (June 13, 2009). Re: Stable Life? (discussion thread) at the ConwayLife.com forums